Injector for a urea-water solution

ABSTRACT

An injector for a urea-water solution includes at least a main body with a fitting for the urea-water solution, a valve with a valve drive and a separate feed pipe for the urea-water solution. The separate feed pipe extends at least partly through the main body.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application, under 35 U.S.C. §120, of copending International Application No. PCT/EP2012/052123, filed Feb. 8, 2012, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2011 010 641.3, filed Feb. 9, 2011; the prior applications are herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an injector for a urea-water solution, with which a urea-water solution can be added, in particular, to exhaust gas systems of motor vehicles. In particular, the injector is used to add liquid urea-water solution in a precisely metered manner to the exhaust gas of an internal combustion engine. It is then possible for the process of selective catalytic reduction (SCR) to be carried out in the exhaust gas system in such a way that nitrogen oxides contained in the exhaust gas can be considerably reduced.

A large number of different injectors have already been proposed for that purpose. However, there is a need for improvement, in particular with regard to cost-effective production of an injector of that type for the automotive industry. A particular problem encountered with previous injectors is that the injectors also have to be able to remain functional in icy conditions. In that regard it should be taken into account, in particular, that the urea-water solution contained in the injector may also freeze under the normal conditions of use of a motor vehicle, and that leads to an increase in the volume of the urea-water solution. That increase in volume may repeatedly lead to blockages in the pipe system as well as malfunctions or destruction of component parts of the injector as a result of the high ice pressure. A further problem encountered with injectors of that type is that they are normally positioned on a hot exhaust gas pipe. That exposure to heat, which is sometimes considerable, may also cause problems with the conveying or metering of urea-water solution. That is true, in particular, if a gaseous supply of urea is to be avoided where possible, or if a threshold temperature of the urea-water solution is not to be exceeded during the feed process. In that regard it should be noted that urea-water solution already starts to evaporate at approximately 110° C., so a controlled precisely metered feed of the urea-water solution may possibly be impeded. Undesirable residues which are difficult to remove may also be formed and may hinder the feed of the urea-water solution to the exhaust gas. In that respect the problem of injector cooling also arises repeatedly.

BRIEF SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide an injector for a urea-water solution, which overcomes the hereinafore-mentioned disadvantages and solves at least some of the highlighted problems of the heretofore-known injectors of this general type. In particular, an injector for a urea-water solution is to be provided which can be produced in a cost-effective manner, is not susceptible to ice pressure of the urea-water solution when frozen, and is adequately protected from the high temperatures of the exhaust gas system.

With the foregoing and other objects in view there is provided, in accordance with the invention, an injector for a urea-water solution, comprising at least a main body with a fitting for a urea-water solution, a valve with a valve drive and a separate urea-water solution feed pipe which extends at least partly through the main body.

The urea-water solution is occasionally also referred to as a reducing agent or reducing agent precursor since the urea-water solution is converted to ammonia after thermolysis or hydrolysis and can then react with the nitrogen oxides in the exhaust gas. In this case, in particular, a 32.5% urea-water solution is used which, for example, is also commercially available under the trademark AdBlue®.

The main body is, in particular, a metal component which may be constructed, on one hand, with passages, surface recesses, contact surfaces for the valve and a cooling system and with ducts for conveyance of the urea-water solution. The main body is, in particular, a solid component which simultaneously serves as a base or a mount for the valve. Although in principle it is possible for the main body to include a plurality of valves and/or a plurality of fittings for the urea-water solution, a configuration with a single valve and a single fitting is still preferred. The fitting is generally constructed as a passage in the main body. Since in this respect the main body is also in contact, at least in part, with the urea-water solution, the material for the main body and/or a coating on contact surfaces exposed to the urea-water solution is/are constructed so as to be resistant to the urea-water solution. The fitting is, in particular, also configured in such a way that conventional connecting joints to the pipes may optionally be integrated therein or fastened thereto.

The valve generally includes a valve element in which the intake pipes and the metered-flow pipes are formed. In addition, a controllably actuable piston may be provided which may be actuated by the valve drive as necessary, in such a way that the fitting, in particular, from the intake pipes to the metered-flow pipe can be opened and closed as necessary (for example as a function of time). For this purpose the valve may additionally include a plug connector for connecting the valve or valve drive to a control unit or controller (electric or signal-conducting) which initiates operation of the valve and thus of the injector as necessary. It is particularly preferred for the valve and the valve drive to be provided as far away as possible from the urea-water solution feed point, i.e. in particular on the side of the main body remote from the exhaust gas pipe. This provides, in particular, the position of the fitting for the urea-water solution which is therefore located between the exhaust gas pipe and the valve.

It is also provided for the injector to have a separate feed pipe for urea-water solution, which extends through the main body, at least in part. The separate feed pipe is therefore configured, in particular, in such a way that it is a separate component which is accommodated, preferably completely, inside the main body. The feed pipe is constructed, in particular, in the form of a small tube, in particular as a small tube extending in a straight line. A metal feed pipe is preferably used which is formed, in particular, of a material different from that of the main body. Furthermore, it is preferred for the separate feed pipe to be positioned predominantly at a distance from the main body in such a way that, in particular, heat conduction between the separate feed pipe and the main body is minimized. Most preferably, at most 10% of the surface of the separate feed pipe is therefore in contact with the main body. The term feed pipe refers, in particular, to the portion of the pipe system for the urea-water solution, which is disposed downstream of the valve, in particular right to the delivery point into the exhaust gas system. Since, in accordance with the above-described variant, the valve is preferably disposed on the side of the main body remote from the exhaust gas pipe, the feed pipe thus extends, for example centrally, through the entire main body.

Such a configuration of the injector alone leads to a considerable improvement with regard to the problems detailed above. On one hand, the valve can thus be protected against the high temperatures of the exhaust gas system, but at the same time boiling of the urea-water solution in the separate feed pipe is also reduced as a result of the low level of heat conduction to the main body.

In accordance with another feature of the injector of the invention, it is also proposed for the separate feed pipe to end in a nozzle plate. This nozzle plate is preferably fastened opposite the valve to the end face of the separate feed pipe. In particular, the separate feed pipe and the nozzle plate form a separately detachable unit. The nozzle plate is distinguished, in particular, in that it is perforated by nozzle orifices which now spray the urea-water solution from the feed pipe into the exhaust gas pipe at a predetermined jet angle. The jet angle may be adjusted, in particular, to allow for the configuration of the nozzle or the spray cone produced therewith. The nozzle plate is preferably constructed in the form of a disc, in particular the space surrounding the separate feed pipe being limited when disposed in the injector, in particular, by the spaced main body. In addition, the nozzle plate may be used to construct a connection or fixing to the injector, positioned at a distance from the separate feed pipe, in such a way that precise orientation of the feed direction is possible. The nozzle plate may also be provided with a material which exhibits low thermal conductivity (for example compared to the main body), is resistant to high temperatures (since it may be in contact with the exhaust gas) and is optionally constructed with a surface which repels urea-water solution. The nozzle plate is thus constructed, in particular towards the exhaust gas system in such a way that any remaining droplets of the urea-water solution thereon can only remain there in the short term. This repellent coating prevents, in particular, (merely) partial evaporation of the urea-water solution and thus the formation of undesirable by-products or deposits. The external face of the nozzle plate preferably exhibits a roughness of less than 0.2 mm and/or a titanium oxide coating.

In accordance with a further feature of the injector of the invention, it is also proposed for the nozzle plate to have at least a plurality of nozzle orifices or to form a protruding end of the feed pipe. It is most preferred for both of these features to be provided. With regard to the number of nozzle orifices, it is preferred for at least two nozzle orifices to be provided, but for the number of nozzle orifices not to exceed, for example, 5. It is most preferred for the nozzle orifices to be oriented or positioned in such a way that the jets of urea-water solution emerging therefrom intersect or collide with one another. A particularly advantageous spray cone can thus be generated. For example, the nozzle orifices are drilled through the nozzle plate in the manner of microducts, preferably by laser drilling.

It is further preferred during use of the injector for exhaust gas to flow where possible in parallel past the nozzle plate (and the nozzle orifices). In order to remove, where possible, all urea-water solution droplets still attached at the end of the metering process, this region should protrude, i.e. in particular it should project at most into exhaust gas pipe. It is sufficient for the protrusion to be very short, for example up to a maximum of 1 mm (millimeter), in particular, even only up to 0.5 mm or up to 0.2 mm. This short protrusion affords the advantage that the heat exposure of the injector in the region of the nozzle plate is simultaneously reduced, in particular, also for the separate feed pipe connected thereto.

In accordance with an added particularly advantageous feature of the injector of the invention, the main body also includes a cooling system which has an inlet and an outlet as well as at least one cooling duct which extends through the main body and is penetrated, in part, by the feed pipe. In other words, this means in particular that the main body includes passages which form an inlet for coolant and an outlet for coolant. It is particularly preferred for the cooling duct to be constructed concentrically about the feed pipe, i.e. in the form of an annular duct, in particular along a predominant portion of the separate feed pipe. Consequently the cooling duct preferably extends in such a way that, starting from the inlet it extends into an inner region of the main body, extends downwards in a region between the feed pipe and the outer wall or else towards the side opposite the valve, is led there in the region of the feed point or nozzle plate centrally inwards again towards the feed axis and then extends at least in part parallel to the feed axis and concentrically around the feed pipe before the cooling duct finally extends towards the outlet again shortly before it reaches the side with the valve. In this respect the cooling system is constructed, in particular, in such a way that a counterflow heat exchanger is formed in the region of the feed pipe, with the coolant flowing towards the valve and the added urea-water solution flowing away from the valve. It is most preferred for the cooling duct to also extend to the nozzle plate where, in particular, it is possible for fresh, cool coolant to flow around the entire region surrounding the separate feed pipe.

In accordance with an additional advantageous feature of the injector of the invention, the main body forms a reservoir for a urea-water solution adjacent the valve, with the valve being disposed movably relative to this reservoir. In particular, the reservoir provides urea-water solution for the valve. The reservoir is thus formed, in particular, between the valve and the main body. It is most preferred for the valve to be disposed in the reservoir, at least in part, in such a way that the reservoir is limited by the main body, the valve and sealing devices, in particular ring seals. The reservoir in which urea-water solution is ultimately stored for the valve during operation is preferably annular. In particular a central circular segment conveys the added portion of urea-water solution towards the separate feed pipe. Since urea-water solution is now generally present in the reservoir and may freeze at low temperatures, the urea-water solution expands in the reservoir. In order to avoid damaging the injector, the valve is disposed movably relative to the reservoir. This means, in particular, that the (entire) valve can be moved away from the main body, in particular along the feed axis. This movement, in particular a stroke movement (for example up to 2 mm, in particular greater than 1 mm) is reversible, i.e. when the urea-water solution thaws again the valve moves back into the normal position. It is thus also ensured that the reservoir always stores the same amount of urea-water solution during operation.

In accordance with yet another advantageous feature of the injector of the invention, the main body forms a reservoir for urea-water solution adjacent the valve, and the valve includes a plurality of intake pipes which open into the reservoir. It is preferred for a plurality of intake pipes to be formed, for example with a uniform pitch in the circumferential direction of the valve, i.e. for example one intake pipe every 120°. The configuration with a plurality of intake pipes affords the advantage that the injector can be used in a versatile manner with regard to final positioning relative to the exhaust gas system. Similarly, a supply to the valve from the reservoir is also ensured if the injector is subjected, for example, to vibrations, etc. during operation. Depending on the position or filling level of the reservoir, it is thus basically ensured that at least one of the plurality of intake pipes is disposed in the region of the reservoir which currently provides urea-water solution. This significantly increases versatility and metering precision during operation.

In accordance with yet a further feature of the injector of the invention, at least one spring element is provided which biases the valve against the main body. In particular, the object of the spring element is to reverse the stroke movement or movement of the valve relative to the main body which occurred after ice formation. In addition, taking into account the reservoir or the amount of urea-water solution stored therein, the spring element may be constructed in such a way that it actually only allows a movement of the valve relative to the reservoir when there is ice formation. The spring element may be disposed, in particular, between a cap and the valve drive, but it is also possible for example to fasten a cap to the main body using fixing devices, with spring elements optionally being provided between the cap and the main body or the fixing devices. In particular the spring elements may be constructed as annular springs or spring washers.

In accordance with yet an added advantageous feature of the injector of the invention, a base with a socket for the main body is provided, and air-gap insulation is formed between the base and the main body in a region around part of the feed pipe. In particular, the object of the base is to orient the main body relative to the exhaust gas pipe and to fix it there securely. The base is also metallic in particular. The socket is configured, in particular, in such a way that the position of the main body is oriented in the base. The heat flux towards the main body can be reduced since a large area of the base is generally fixed to the hot exhaust gas system. For this reason it is proposed that, in particular, the lower region of the main body facing the exhaust gas pipe be thermally decoupled. In this case, it is preferred to mainly avoid an unwanted heat flux from the exhaust gas pipe to the urea-water solution on one hand (by avoiding boiling) and to avoid an unwanted strong cooling of the exhaust gas pipe on the other hand (by reduction of the risk of depositions on the inner side of the exhaust gas pipe). For this purpose an annular or else cup-shaped cavity is formed in particular between the base and the main body and forms air-gap insulation. It is thus preferred, in particular, for contact between the main body and the base to be provided directly only on the side of the base remote from the exhaust gas pipe. In particular it is also preferred for only linear contact or repeated point contacts to be formed between the feed pipe or the nozzle plate and the base in the urea-water solution delivery region. The gap between the base and the nozzle plate may optionally also be sealed by sealing devices or spacers disposed in the air gap.

In accordance with yet an additional feature of the injector of the invention, at least one spacer is provided in the at least one air-gap insulation. The spacer serves in particular for exact orientation or simplified assembly of the base and the main body relative to one another. This spacer may be constructed for example as a washer, as a metal seal, as a spring element or the like. The spacer is shaped, in particular, in such a way that heat conduction from the base to the main body is slight. In particular, materials exhibiting low thermal conductivity and/or components having small areas of contact with the base and the main body are used. It is most preferred for merely a single spacer to be provided which forms a guide for the main body in the socket in the base.

In accordance with a concomitant feature of the invention, the fitting for the urea-water solution be constructed with a closable exit. An injector of this type is generally disposed downstream of a conveying device for urea-water solution. This means that urea-water solution is stored at increased pressure, for example at a pressure of from 5 to 8 bar, in the connecting pipe from the conveying device (for example a pump) to the injector and therefore also in the region of the fitting in the main body. The object of the closable exit is to allow this pressure to be relieved at a predetermined position, for example when the injector needs to be serviced or replaced. In particular, the volume of urea-water solution under pressure in the injector can thus be depressurized and can flow out through the exit, at least in part. The exit is formed, in particular, as a spur passage to the fitting and is closed by a stopper, for example a sealing screw.

Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the features recited individually in the claims may be combined with one another in any technologically feasible manner and illustrate further configurations of the invention.

Although the invention is illustrated and described herein as embodied in an injector for a urea-water solution, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, partly-exploded, perspective view of an injector for a urea-water solution;

FIG. 2 is an enlarged longitudinal-sectional view of an injector for a urea-water solution;

FIG. 3 is a further-enlarged sectional view of a main body and a base in an assembled state;

FIG. 4 is a longitudinal-sectional view of a component formed by a separate feed pipe and nozzle plate;

FIG. 5 is an enlarged sectional view of a portion of FIG. 4;

FIG. 6 is a sectional view of a portion of an air-gap insulation between the base and the main body;

FIG. 7 is a sectional view of a portion of an injector for a urea-water solution with a closable exit; and

FIG. 8 is a block diagram of a motor vehicle with an exhaust gas after-treatment system including an injector for a urea-water solution.

DESCRIPTION OF THE INVENTION

Referring now in detail to the figures of the drawing for explaining the invention and the technical field in more detail by showing particularly preferred structural variants to which the invention is not restricted, and first, particularly, to FIG. 1 thereof, there is seen a partly-exploded perspective view of a variant of an injector 1 for a urea-water solution. An adapter for pipe fittings 28 is shown in broken lines on the right-hand side of FIG. 1, in which upwardly directed pipe fittings form, for example, a cooling water supply and drain and a central linear pipe fitting represents a connecting pipe for the urea-water solution. These pipe fittings 28 can be conveniently disposed on a main body 2 of the injector 1, for example by using screws as shown in this example. The pipe fittings 28 for the cooling system open into an inlet 11 or outlet 12 provided for this purpose. A fitting 3 is formed in the main body 2 opposite the pipe fitting 28 for the urea-water solution, in particular as a passage. The main body 2 is a cast part. In order to prevent the introduction of solid constituents into the injector 1, a filter 27 is also provided in the region of the fitting 3 and, in particular, includes a coarse filter (for example with a mesh size of greater than 100 μm) and a fine filter (for example with a mesh size of less than 50 μm), i.e. it is made up of several layers. The urea-water solution consequently flows into the injector 1 through this fitting 3 and the filter 27.

A valve 4 is also indicated above the main body 2 and, in this instance, is disposed beneath a cap 24. The cap 24, in which the valve 4 is accommodated with an associated plug connector 26, is biased against the main body 2 by fixing devices 25. It is also optionally possible for spring elements to be provided between the fixing devices 25 and the cap 24 in such a way that, in particular when the valve 4 moves, the cap may optionally also effect a compensating movement, in particular in the form of a stroke, relative to the fixing devices 25.

This component may now be inserted into a base 17 which is conventionally connected to an exhaust gas pipe. For this purpose the base 17 includes an inner socket 18 so that the main body 2 is positioned with a precise fit and is circumferentially oriented relative to the base 17.

FIG. 2 shows an embodiment of an injector 1 for a urea-water solution. The fitting 3 for the urea-water solution is again shown to the right of FIG. 2. A direction of flow 30 of the urea-water solution through the injector 1 is also indicated by black arrows. The filter 27 is in turn shown in this fitting 3 and in this instance is curved against the direction of flow 30, which is particularly advantageous since any incoming solid constituents are deposited in the outer edge region and therefore do not impede the flow centrally. The filtered urea-water solution then flows on through a constricted duct portion towards the valve 4. The main body 2 is configured in such a way that a reservoir 14 is formed between the valve 4 penetrating into the main body 2 and the end of the duct portion from the fitting 3 for the urea-water solution. In this instance the reservoir 14 is substantially circular and is limited or sealed internally and externally by ring seals 35 (O-rings). The valve 4 includes a plurality of (namely three) intake pipes 15, with which the urea-water solution can be drawn in. The valve itself (with a valve flap or valve pin) is disposed above the intake pipes 15 and is actuable by a valve drive 5. Control signals or power supply for the valve drive 5 are fed through the plug connector 26, which protrudes from the cap 24. The plug connector 26 is thus also far removed from the exhaust gas pipe and is therefore exposed to slight heat. If the valve 4 is now actuated, an entrance to a feed pipe 6 is opened in such a way that a predetermined amount of urea-water solution can then flow into the feed pipe 6 until it issues again from the feed pipe 6 at the opposite end, in particular into the exhaust gas flow of an internal combustion engine. The separate feed pipe 6 is disposed flush on the valve 4, and in particular is surrounded by the inner ring seal 35. A welded joint may optionally be formed between the separate feed pipe 6 and the main body 2 in the region of a contact face facing the valve 4.

Since urea-water solution can now collect in the reservoir 14, there is a risk that substantial pressure could build up if the urea-water solution freezes. For this purpose, the valve 4 (together with the valve drive 5) is formed so as to be movable relative to the main body 2 and the cap 24. If the pressure inside the reservoir 14 increases, it is possible that the valve 4 and the valve drive 5 will perform a displacement movement, in particular in the manner of a stroke 22. The outer ring seal 35 thus ensures that the reservoir 14 is still tight. This compensating movement or stroke 22 is made possible or adjusted by a spring element 16, with which the valve (together with the valve drive 5) is biased against the main body 2. If the pressure is too great as a result of ice formation, the valve 4 moves upwards, and if the frozen urea-water solution thaws again and the pressure there is then reduced, the spring element 16 moves the valve 4 back downwards again.

A cooling system 10 is also illustrated in the lower region of the main body 2, with a coolant flow direction 29 being indicated by white arrows in this case. The coolant thus flows through the inlet (not shown therein) into the inner regions of the main body 2 until it reaches an illustrated or visible part of a cooling duct 13. Referring to FIG. 2, the coolant flows downwards, at a distance from the feed pipe 6, in the direction of a delivery point or a hottest point for the urea-water solution, where it is diverted (virtually in the opposite direction) and then flows back concentrically in the direction of the valve 4 over the predominant portion of the separate feed pipe 6 in the manner of a sheathing jet. Shortly before the valve 4 is reached, the cooling duct 13 leaves the region around the separate feed pipe 6 and extends further toward the outlet (which is not shown). A counterflow heat exchanger is thus formed inside the main body 2, irrespective of the configuration of the remainder of the injector, and ensures that the urea-water solution disposed in the feed pipe 6 is reliably cooled and that boiling of the urea-water solution can be prevented. In order to ensure that this also occurs virtually as far as the delivery point for the urea-water solution, the cooling duct 13 extends, in particular, as far as a nozzle plate 7 which forms a protruding end 9 of the injector 1. Therefore, even this portion, which is exposed to high temperatures, can be reliably cooled.

Furthermore, the base 17 is also illustrated therein, with air-gap insulation 20 being formed circumferentially about the main body 2 and also the separate feed pipe 6. On one hand, a coolant jacket and on the other hand, an air-gap jacket are consequently provided around the feed pipe 6 in a region 19 close to the delivery point, in such a way that active and passive thermal insulation are provided in the circumferential direction concentrically to the feed pipe 6.

FIG. 3 is a cross section through a configuration in which a main body 2 is inserted into a base 17. In particular, FIG. 3 is an enlarged view of the air-gap insulation 20. It can be seen that the main body 2 is actually only in heat-conducting contact in the region of the end face opposite the exhaust gas pipe. The air-gap insulation 20 and the concentric cooling duct 13 extend about a central feed axis 31, over virtually the entire height of the base 17, but at least over 70% or even over 80% of the height of the socket in the base 17. The air-gap insulation 20 is strongest (for example as a result of a large distance between the base 17 and the main body 2) where the base 17 is solid in the vicinity of the exhaust gas pipe since this is where a high thermal capacity is provided for the waste heat of the exhaust gas system. The air-gap insulation 20 is thus particularly pronounced, precisely in this region 19.

FIG. 4 illustrates a component formed of a separate feed pipe 6 for urea-water solution and a nozzle plate 7 to be positioned in the vicinity of the delivery point, i.e. opposite the valve (which is not shown). The separate feed pipe 6 may include a widening 38 in the vicinity of end faces, for example in order to compensate for positional tolerances. A pipe volume 32 inside the feed pipe 6 should be kept low if possible, i.e. a small pipe cross section 33 should be produced, in particular. For example, the pipe volume 32 may be less than 100 mm³ or less than 60 mm³. An individual nozzle plate 7 is thus formed on an end face and is rigidly connected (welded) to the feed pipe 6. The nozzle plate 7 includes a recess 49 around the region of contact with the feed pipe 6, enabling the coolant to flow as close as possible to the end face of the feed pipe 6. In particular, it is thus also possible to cool nozzle orifices 8 formed in the nozzle plate 7 at the end of the feed pipe 6. An enlarged view of a portion thereof is shown in FIG. 5.

FIG. 5 shows the above-mentioned portion of FIG. 4. It can be seen that, at the front, the nozzle plate 7 includes a welded seam 37 connecting it to the end face of the feed pipe 6. The welded seam 37 may also be constructed by spot welding. The nozzle plate 7 rests flush against the end face of the feed pipe 6 and also terminates the end of the feed pipe, in the circumferential direction. Two nozzle orifices 8, which extend at an inclination to the feed axis 31, are shown adjacent the widening 38 in this case. The nozzle orifices 8 are configured, in particular, in such a way that a jet angle 36 is produced between them which is preferably less than 20°. The nozzle orifices 8 are preferably oriented in such a way that urea-water solution jets thus formed meet after leaving the nozzle plate 7. A particularly effective spray pattern with very small droplets of urea-water solution can be produced with colliding jets of this type, making it possible to achieve improved distribution of the urea-water solution in the exhaust gas.

FIG. 6 shows a further portion of an injector 1 for a urea-water solution. In this case a variant of an air-gap insulation 20 is again shown in particular. Similarly, in order to now ensure that the main body 2 is securely positioned in the base 17, and with little movement, while heat conduction from the base 17 to the main body 2 is simultaneously reduced, the air-gap insulation 20 is formed with the outlet 12. In this case a spacer 21 is constructed in the form of a metal profiled part 39 which accommodates the main body 2 in the manner of a basket. The metal profiled part is, in particular, a type of spring element which is shaped in such a way that it only forms linear contacts 40 with the main body 2 or the nozzle plate 7 on one hand, and the base 17 on the other. The linear contacts 40 make it possible to orient the main body 2 or the nozzle plate 7 relative to the base 17, but they do not overcome significant heat conduction through the metal profiled part 39.

FIG. 7 is a further cross section of an injector for a urea-water solution, with only a lower partial region being shown in this case. The separate feed pipe 6 penetrating the main body 2 is shown centrally with the nozzle plate 7. In this case the air-gap insulation 20 is also achieved by providing a washer 34 as a spacer. The washer 34 may be formed of thermal insulator and/or a sealing material toward the exhaust gas pipe. Corresponding air-gap insulation 20 can thus be achieved between the nozzle plate 7 and the base 17 to the delivery point, where the nozzle plate 7 penetrates the base 17. The air-gap insulation 20 can thus also be maintained when the main body 2 and base 17 are assembled by using the fixing devices 25.

An exit 23 is also illustrated on the right-hand side of FIG. 7, which allows communication with the fitting 3 in the main body 2 for the urea-water solution. This exit 23 can be closed with a stopper 41, in particular a threaded screw. The stopper 41 may be removed for disassembly or servicing of the injector, in such a way that the volume of urea-water solution disposed in the fitting 3 can be removed through this exit 23.

FIG. 8 illustrates a particularly preferred field of application of the injector 1 for a urea-water solution. A motor vehicle 50 with an internal combustion engine 42, for example a diesel engine, is illustrated schematically. The exhaust gas produced in the internal combustion engine is conveyed to an exhaust gas system 43 which includes at least one exhaust gas pipe 44. In order to carry out the SCR process, a reducing agent (in this case ammonia) is first added to the exhaust gas and the mixture is then fed through an exhaust gas treatment unit 45, in particular, an SCR catalytic converter. The nitrogen oxides contained in the exhaust gas can then undergo catalytic conversion in the exhaust gas treatment unit 45 at an appropriate temperature of the exhaust gas and with selective metering of urea-water solution to the exhaust gas upstream of the exhaust gas treatment unit 45. The ammonia required for this process is produced from the urea-water solution by thermolysis and/or hydrolysis, preferably in the presence of exhaust gas. This solution is in turn fed through the injector 1 as necessary. The urea-water solution may be stored, for example, in a tank 46 and may be conveyed to the injector 1 through a connecting pipe 48 and a conveying device 47 including, in particular, a pump. Operation of the conveying device 47 and/or of the injector 1 may be controlled as necessary by a superordinate control unit or controller. This may take into account test data relating to the exhaust gas composition, exhaust gas temperature and/or the condition of the internal combustion engine. This control unit may also be part of an engine control system.

The invention thus discloses a practical, precisely-metering and freeze-proof injector which can be produced in a cost-effective manner. 

1. An injector for a urea-water solution, the injector comprising: a main body having a fitting for the urea-water solution; and a valve having a valve drive and a separate feed pipe for the urea-water solution, said separate feed pipe extending at least partly through said main body.
 2. The injector according to claim 1, which further comprises a nozzle plate in which said separate feed pipe ends.
 3. The injector according to claim 2, wherein said nozzle plate has at least a plurality of nozzle orifices.
 4. The injector according to claim 2, wherein said nozzle plate forms a protruding end of said separate feed pipe.
 5. The injector according to claim 1, wherein said main body includes a cooling system having an inlet, an outlet and at least one cooling duct extending through said main body and being partly penetrated by said separate feed pipe.
 6. The injector according to claim 1, wherein said main body forms a reservoir for the urea-water solution adjacent said valve, and said valve is disposed movably relative to said reservoir.
 7. The injector according to claim 1, wherein said main body forms a reservoir for the urea-water solution adjacent said valve, and said valve includes a plurality of intake pipes opening into said reservoir.
 8. The injector according to claim 1, which further comprises at least one spring element biasing said valve against said main body.
 9. The injector according to claim 1, which further comprises a base with a socket for said main body, and air-gap insulation formed between said base and said main body in a region around a part of said separate feed pipe.
 10. The injector according to claim 9, which further comprises at least one spacer disposed in said air-gap insulation.
 11. The injector according to claim 1, wherein said fitting for the urea-water solution has a closable exit. 